Binocular double vision is a serious and often intolerable visual condition. Double vision arises when there is an acquired, decompensated, and/or non-suppressed strabismus. Strabismus refers to the misalignment of the eyes so that one eye deviates in, out, up, down, rotationally, or a combination thereof relative to the other eye.
Many treatments have been successfully used over the years to correct or reduce double vision. These include the use of medications, lenses, patching, surgery and prism.
Of particular difficulty is the treatment of a cyclo deviation where one eye is rotated either clockwise or counterclockwise relative to the other eye. Most commonly, the rotationally deviating eye is caused from damage to the Fourth Cranial Nerve (CNIV) and/or its innervated muscle, the Superior Oblique. The function of this muscle is to lower the gaze of the eye when it is at adducted (turned inward) and to incyclo rotate the eye in all positions except for adduction.
When the deviation of an eye is linear, i.e., turned in, out, up, down, or on an angle, prism can be effectively used to compensate for the amount of the deviation. Exceptions are where there is a paretic or paralytic muscle involved, and then the amount of deviation varies with the direction of gaze. In these conditions prism is still beneficial, but may not be fully compensatory. When there is a rotational deviation, known applications of prisms used in lenses for eyeglasses are ineffective.